Plural stage cooling machine



Jan- 8 1952 f M. s. w. RUHEMANN PLURAL STAGE COOLING MACHINE Filed Oct. 12, 1948 MNT NNI mw .1 --.1.2.5-4 :V y luv'Y 2 1V r om n? 2\ Q 2 2- J n..

Patented Jan. 8, 1952 v1I4U-IAL STAGE COOLING MACHINE Martin Siegfried William Ruhemann, London, English@ `assigner to Petrocarbon Limited,

London, England Application October 12, 1948, Serial No. 54,028 In Great Britain October 20, `1941' i claims. (G1- fia-115.2

This invention relates to cooling processes and machines and more particularly to compression refrigerating processes and machines in whicha mixture of two or more refrigerante of different boiling points is used.

It has been proposed to use a twoestage refrigf. erating cascade in which the iirst stage is a dif,.-` fusion-absorption machine and the second stage a compression machine. It has further been proposed to use in the second stage .of such a ma.- chine a mixture of refrigerante consisting pref.- erably of a mixture of two or more hydrocarbons having different boiling points. This arrangement was shown to have two peculiar advantages in that firstly a lower temperature can generally be reached by the choice of a suitable mixture Ain the second stage than by the use of a pure refrigerant which can be condensed at the temperature of the nrst stage and thatsecondlyirefrigeration can be .effected over a wide :temperature interval byusing mixed `refrigerante, instead-of at one low temperature alone, `a-s :in `the case of a pure refrigerant.

In the arrangements hitherto describedfor the use of mixed refrigerants, whether in a singlestage compression machine or as vthe second sta-ge of a two-stage machine, the lowest ternperature obtainable is the boiling point, at the lowest obtaining pressure, of vthe mixture of refrigerants having the composition at which it enters the machine. Moreover this composition, and hence the lowest temperature obtainable, cannot be varied beyond a certainlimit in view oi` the necessity inthe known arrangements of 4liquefying the whole of the mixture with atmospheric air or cooling water or in the first stage of the machine.

In order to obtain still lower temperatures it is necessary, according to existing proposalsfto add a third stage to the machine, thus makingthe arrangement more complicated and costly.

' It is an object of the present invention -to provide a process and machine free of the above disadvantages, that is to say, a process which enables lower temperatures to be reached in acompression stage using `mixed refrigerante, both the case of a single-stage process and in the oase of .cascade refrigeration, and a :machine operating by theaboye process. In other words or further :an objectof the invention is reproduce-with a compression refrigerating machine using mixed refrigerants lower temperatures than could otherwise be obtained with the same refrigerant mixture between the same pressure limits while at `the same time retaining the characteristic advantage of `refrigeration with mixed refrigerants, namely, the absorption of heat or the production of cold over a wide interval of low temperatures.

In the compression refrigeration process of the invention which operates with a mixture of gaseous refrigerants of different boiling points, the condensation of the gaseous mixture after Ycorn-4 pression takes place in atleast two steps and 'the liquid portion and the gaseous portion resulting from the first partial condensation step are physically separated from each other (i. e. are `passed into separate conduits), the gaseous portion being condensed in one or more subsequent condensation steps.

The cooling required for the rst partial condensation step may be effected by means of atmospheric air or of cooling water when `the process is carried `out in a :single stage machine. .On the other hand, if the process forms a second or later stage of a cascade refrigeration system. the cooling for the first partial condensation step .may be effected `by the refrigerant of the rst or preceding stage of the cascade system.

The partial condensation step forming part of the process of the invention and referred .to .above and hereinafter may be carried .out in .one or more Acooling units and comprises the whole step from its commencement down to the point at which physical separation of the liquid and gaseous portions takes place.

i The compression refrigeration process of the inventionmay be operated with two refrigerants, for example, ethylene and propane `for a single stage process or ethylene and methane when it forms the second sta-ge of a cascade refrigeration system. In such case, the gaseous portion left after the `iirst partial condensation step is generally completely condensed whilst under pressure in a second condensation step by cooling in thervmalcontact with at least part of the liquid portionevaporating at a lower pressure. The last condensed portion is then evaporated at a lower pressureto produce cold over a range of temperature and rthus` performs the refrigerating duty required.- f e 3 The condensation of the gaseous portion may be eected by the evaporation of the whole of the liquid portion or only part thereof. The proportion of the gaseous mixture condensed in the first condensation step is adjusted to meet eitherY of these requirements. In the case where the evaporation of only a part of the liquid portion is used to condense the gaseous portion, the evaporation of the remaining part of the liquid portion may be used to perform part of the refrigerating duty of the process.

The invention also consists of a compression refrigeration machine for operation with a mixture of gaseous refrigerants of different boiling points which comprises a compressor, cooling means for partially condensing the gaseous mixture after compression, a condenser-evaporator having a coil passing therethrough, a conduit for leading the condensate from the cooling means through an expansion valve to the exterior of the said coil and a second conduit for leading the gaseous portion from the cooling means `tothe* Y interior of the said coil.

By the utilisation of the compression refrig- Y point, at the lowest obtaining pressure, ofV this .i

new gaseous portion which will be lower than that of the initial mixture. y

Moreover, since inthe process of the invention the whole of the gaseous mixture of refrigerants is not liquefied in lone step, greater scope is provided in choosing the composition of the mixed refrigerants. More especially it enables a mixture of refrigerants to be used containing a higher percentage of more volatile components than would otherwise be the case.

In one method of carrying out the process of the invention, a mixture of gaseous refrigerants of suitable composition is compressed to a pressure at which a certain portion of it can be condensed in heat exchange with atmospheric .air or cooling water or, if the mixed refrigerant is used in the second stage of a cascade, by the refrigerant of the first stage of the machine. The liquefied portion of the mixed refrigerant, which will be richer in the less volatile components, and the gaseous portion, which will be richer in the more volatile components, are then separated and fed into separate conduits, i. e. are physically separated from each other.

The gaseous portion of the mixed refrigerant, with or without suitable pre-cooling, is partially or completely liquefied in thermal contact withV the liquid portion evaporating at a llower pressure. y

Thereupon the liquid resulting from this second condensation step is itself expanded to a lower pressure, preferably atmospheric pressure, there-V One form of refrigerating apparatus con-,g

f a pressure, which may be 20 atmospheres, into the ririgerating system. The amount of gases pumped into theplant is estimated by means of the gauge 3l and when sufcient has been transferred the valve I2 is closed and the storage tank is then isolated from the system. The gases leaving the compressor I3 rst pass up through the coil I4 of after-cooler I5 in which they are cooled by water entering at I6 and leaving at I1.

They then pass down through the coil I8 of water cooler` I9 in which they are further cooled and partially condensed by water entering at 20 f and leaving Vat 2l'. The extent of the condensation is determined by the initial composition of the gaseous mixture, the working pressure and the temperature of the cooling water. The droplets of liquid formed in coil I8 are swept on by the remaining gases downwardly through thev coil 22 of the vessel 23 where further cooling, and hence further condensation, is effected by cold gases returning from a later part of theV system to the compressor I3 and entering at 24 and leaving at 25. VThe liquid and gaseous portions resulting from the partial condensation stepcarried out in vessels I9 and 23 are physically separated at the lower end of vessel 23 by leading off the liquid portion through pipe 26 at the bottom and leading off the gaseous portion through pipe 21 at the side.

In order to minimise entrainrnent of the fine liquid droplets by the gaseous stream, the two portions may be passed through an agglomerator 28 which causes the droplets to coalesce .as they pass into the lower end of the vessel 23, but the use of an agglomerator is not essential. When used, the agglomerator 28 is a vertical cylindrical ring fitted with a tightly wound vertical helix of thin metallic ribbon having a closely spaced ne corrugation. The liquid portion leaving through the pipe 26 then passes down through the coil 29 of the sub-cooler 30 in which it is cooled below its boiling point at theworking pressure by returning cold gases which pass upwardly through cooler 30, entering at 33 and leaving at 34 as shown by the dotted line. The cooled liquid then divides intotwo streams, one passing through expansion valve 35 and the other throughexpansion valve 36 expanding in each case to a lower pressure which may be atmospheric pressure. The liquid which has passed through valve35 is then led into the condenser-evaporator v3'1 in which it ows downwardly over the coil -38 and evaporates at the lower pressure, cooling the load which is led into the bottom ofV the coil 38 through valve 39. The liquid passing through valve 36 similarly evaporates at the lower pressure in condenser-evaporator 40 where it cools the gaseous portion coming from vessel 23 and passing upwardly through the coil 4I. gaseous portion is condensed in passing through condenser-evaporator 40 and the liquid is passed through the expansion valve 42, expanding'to ai lower pressure, and at this lower pressure, which,

may be atmospheric pressure, into the condenserevaporator 43 where it flows downwardly over the coil 44 andY evaporates'fto .further cool the load;`

This

which passes from the coil 38 upwardly through the coil 44 of Vcondenser-evaporator I3. The evaporating Aliquids .pass downwardly over the coils .in each of the condenser-evaporators 431 l and 43, 4and the .gases formed also pass `downwardly and thenpass upwardly 'through the `core of the condenser-evaporator in each case to leave at the top of each condenser-evaporator. The cold gases leaving the eendenser-evaporators 31, 40 and 43 at points 145 it :and 41 respectively are passed together into sub-cooler 39 at point `33 and pass upwardly through the sub-cooler `30 and thence-through vessel 23 to the compressor l,3,\as indicated bythe dotted line `and arrows. Thefdotted line indicates the flow ofirefrigerants at the lower pressurei Operating the apparatus described `above` as a single stage refrigeration machine with a mixture of ethylene and propane in equimolecular proportions and with a working pressure of 20 atmospheres absolute and a return pressure of l atmosphere absolute, cooling water being supplied at C., the following results were obtained:

Inlet temperature of cooling medium in vessel 4? 92 Outlet temperature of cooling medium in 4 vessel 43 '70 Inlet temperature of cooling medium in vessel 37 70 Outlet temperature of cooling medium in Vessel 3'7 55 Thus cold was supplied to the load passing through vessels 31 and 43 over a temperature interval of 92 C. to 55 C. The cold produced was found to be 55.2 gals per kg. of mixed refrigerants passing through the compressor.

The gradient over which cold is supplied may be broken into several stages so that if the load is a mixed gaseous one the liquid fractions formed at various temperatures can be led off whilst the remaining gaseous part is allowed to pass further along the exchanger to be taken off at some lower temperature.

In the apparatus described and illustrated, the liquid portion having passed through coil 29 of sub-cooler 30 is divided into two streams, but the working conditions may be so chosen that the amount of refrigerants condensed in coolers I9 and 23 is such that the evaporation of the whole of this condensate at the lower pressure is required to condense the gaseous portion passing through the coil 4I. In this case, the condenserevaporator 31 may be omitted and the whole of the refrigerating duty is performed in condenserevaporator 43. The apparatus described and illustrated is a single stage compression refrigeration machine but the process of the invention can obviously be used to advantage in a two stage cascade refrigeration system. In the latter case the apparatus illustrated may comprise the second stage of the cascade refrigeration system, the Water cooler I9 being replaced by a condenserevaporator into which a refrigerant which has been compressed and liqueed by cooling in the first stage is fed through an expansion val-ve and evaporated, the gas resulting from this evaporation being returned to the compressor of the rst stage.

It is also possible with the process of the invention to use a mixture of three gaseous refrigerants. for example, propane, ethylene, and methane. The working pressure may then be arranged so that .inthe initial partial'condensation ,step a smaller portion of `the Vrefrigerant mixture is condensed. i The gaseous and liquid portions thus formed are 'physically separated and about half ofthe gaseous `portion is lcondensed by` cooling in thermal contact with lat least part of the liquid portion evaporating at a lower pressure. The gaseous and liquid portions resulting from thesecond condensation step are also physically separated and the gaseous portion is completely liquefied by cooling in thermal contact with atleast part `of `the condensate :from the second condensation step evaporatirrg at a lower pressure. The nal condensate is then expandedto a.. lower pressure and vevaporated to produce cold over a range of temperature. Any condensate resulting from the, first condensation step and not evaporatedin the second condensatior'i step is evaporated at a lower pressure to perform part of the refrigerating duty of the process. Similarly any condensate resulting from the second vcondensation step and not evaporated in the final condensation step is evaporated at a lower pressure to perform a further part of the refrigerating duty of the process.

Such a system would enable another exchanger to be added which would cool the load from say 90 C. to 120 C. and hence one single refrigerating unit can handle a fairly complex mixtur of gases.

I claim:

1. A compression refrigeration machine for operation with a mixture of gaseous refrigerants of diierent boiling points, which comprises a compressor, cooling means for partially condensing the gaseous mixture after compression, a condenser-evaporator having a coil passing therethrough, a conduit for leading the condensate from the cooling means through an expansion valve to the exterior of the said coil and a second conduit for leading the gaseous portion from the cooling means to the interior of the said coil.

2. A closed-circuit compression refrigeration system for supplying the cooling requirements of a system outside said closed-circuit system, and

operating with a mixture of normally-gaseous refrigerante of different boiling points, which comprises in combination a compressor having a suction side and a pressure side for compressing said gaseous refrigerants, heat-exchanging means for cooling the compressed gaseous mixture thereby partially liquefying said mixture, means for separating the resulting liquid fraction from the gaseous fraction, means for further cooling the separated liquid fraction, an expansion valve,

means for conducting at least part of the subcooled liquid fraction through said expansion valve and then in indirect thermal contact with the separated gaseous fraction thereby causing the latter to condense, a second expansion valve, means for passing the resulting condensate through said second expansion valve and then in heat exchanging relationship with said outside system to supply the cooling requirements .-j thereof and conduit means for returning the named expansion Vvalve and fused tocondense the separated gaseous lfraction, means being provided to pass the remainder of the liquid fraction through another yexpansion valve and then in heat exchanging relationship with'said outside system to supply cooling thereto over a temperature range above thatsupplied by the condensed gaseous fraction. 1

MARTIN SIEGFRIED WILLIAM RUHEMANN.

REFERENCES CITED The following references are of record in the `le of this patent:

UNITED STATES PATENTS 8 Number Name Date `'2,278,889 Maiuri Apr. 7, 1942 2,341,320 Hall Feb. 8, 1944 2,453,823` Williams NOV. 16, 1948 2,456,386 Cooper Dec. 14, 1948 2,458,560 VBuehanan Jan. 11, 1949 OTHER REFERENCES The Separation Of Gases by M. Ruhemann,

10 pp. 128 to 134, Clarendon Press 1940.

Master Service Manual C-3 by K. M. Newcum, page 249. Published by Business News Publishing Company, 1938.

Refrigerating Data Book, 1942, pages 5, 6 and 15 '7. Published by American Society of Refrigerating Engineers, 50 West Fortieth Street, New York, New York. l Y 

